| Research Abstract |
Complexation of pyridine (py), 3-methylpyridine (3Me-py) and 4-methylpyridine (4Me-py) with bivalent transition metal ions has been investigated by calorimetry and spectrophotometry in N,N-dimethylformamide (DMF) and acetonitrile (MeCN). It was revealed that the structure of the [ML_4] ^<2+> complexes (M=Co, Ni, Cu) is octahedral, while that of the [ZnL_4] ^<2+> complex is tetrahedral. This is consistent with our EXAFS (extended X-ray absorption fine structure) measurements showing that the solvation structure of the manganese (II), coblt (II) and nickel (II) ions is six-coordinate octahedral in 4Me-py and 3Me-py, while that of the zinc (II) ion is four-coordinate tetrahedral in 4Me-py. Complexation of 18-crown-6 with alkali-metal, alkaline earth metal and ammonium ions in various aprotic solvents and water has been investigated by titration calorimetry. The complexation of 18-crown-6 is more favorable in the aprotic solvents than in water. The reaction enthalpies and entropies, howeve
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r, differ much among the solvents. Thus the complexation of 18-crown-6 reflects the different solvation of 18-crown-6 and also the different degree of solvent strucutre. Complexation of 18-crown-6 with alkaline earth metal ions in DMF-MeCN mixtures has also been investigated by calorimetry and it was indicated that the metal ions are preferentially solvated with DMF molecules and 18-crown-6 is preferentially solvated with MeCN molecules in DMF-MeCN mixtures.
A spectrophotometric method was developed for the determination of ultratrace amounts of copper (II) based on its catalytic effect on the oxidative coupling reaction of 3-methyl-2-benzothiazolinone hydrazone with N-ethyl-N- (2-hydroxy-3-sulfopropyl) -3,5-dimethoxyaniline to produce an intensely colored dye in the presence of hydrogen peroxide. In this reaction, pyridine acted as an effective activator for the catalysis of copper (II). A flow injection analysis (FIA) method was developed for the simultaneous determinations of vanadium (V) -vanadium (IV), of iron (III)-vanadium (V) and of iron (III) -chromium (VI) using a single injection. In the presence of 1,10-phenanthroline (phen), iron (III) is easily reduced by vanadium (IV) to iron (II), followed by the formation of a red iron (II) -phen complex (lambda_<max>=510 nm), which shows a positive FIA peak corresponding to the concentration of iron (III). On the other hand, in the presence of diphosphate reductions of vanadium (V) and/or chromium (VI) with iron (II) occur easily and a negative FIA peak at 510nm corresponding to the concentration of vanadium (V) and/or chromium (VI) is obtained. Less
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